This invention relates to a method of detecting scarfs appearing on the surface of continuously cast steel strip such as a slab or billet, while they remain hot, by means of a remote contactless process.
A continuous casting method has recently achieved a prominent progress as a substitution for the known blooming process. In this case, the customary practice of detecting scarfs occurring on the surface of a steel strip in the process of being continuously cast is to cool the strip to room temperature and examine the surface by the naked eye or any other unreliable means to find scarfs, if any, appearing thereon. Consequently, such prior art examination process has the drawbacks that the examination step consumes a long time, and leads to the possibility of disqualified product being manufactured with the resultant decline in the yield; and, if scarfs are detected by examination, the product has to be heated again after removing the scarfs, thus resulting in considerable heat loss.
Another examination method known to date is to observe the surface of a hot steel strip in the process of being continuously cast, with notice taken of the fact that the steel strip travels at a lower speed than in the blooming method. However, this proposed examination method has been little put into practice because of the drawbacks that since an examination operator can not approach a hot steel strip, the examination step is accompanied with considerable difficulties and risks and has low reliability.
No apparatus has yet been developed which examines the surface of a steel strip in the process of being continuously cast for detection of scarfs appearing thereon in any desired spot, for example, in a cooling chamber in which a large number of support rollers are horizontally arranged. Hitherto, examination has generally been undertaken in a shop where a plurality of withdrawal rollers or straightening rollers are set. The reason is that examination in the cooling region is encountered with great difficulties due to the ejection of large volumes of cooling water from a series of sprays and the resultant generation of steam.
Where, however, a steel strip in the process of being continuously cast happens to indicate such a defective surface condition as demands an instant care, it is preferred to detect such defect as soon as possible, supply data on the result of said detection to, for example, a control section for adjusting the casting rate, and to take early countermeasures such as adjustment of the casting rate of a steel strip which constitutes at least one of the main causes leading to the growth of scarfs. To date, however, no apparatus has been known which meets the above-mentioned requirements, relative to the continuous casting of a steel strip.
It is accordingly the object of this invention to provide a compact apparatus and an effective method for accurately and sufficiently detecting scarfs appearing on the surface of a steel strip such as a slab or billet in the process of being continuously cast at any desired spot, or preferably in a cooling chamber substantially without being affected by cooling water or steam.